1. Field of the Invention
The present invention relates to a packet switch and a cell switch (hereinafter, simply referred to as a switch) for use in data transfer on a network and, more particularly, to a switch and an input port thereof for conducting switch scheduling according to priories set at data.
2. Description of the Related Art
For data traffic on Internet, none of QoS (Quality of Service) of traffic called best effort is conventionally provided with respect to band, delay, fluctuation, etc. In other words, a switch which transfers IP packets, when receiving a packet only transfers the packet by QoS which can be provided at the time of the packet reception but provides no QoS assurance.
Under these circumstances, the advent of such protocols as RSVP (Reservation Protocol) and DiffServ (Differentiated Service) makes it possible to assure QoS of traffic as a protocol in the field of Internet.
Also with respect to a switch, technique is proposed which enables assurance of QoS with traffic classified according to QoS. One of conventional techniques of this kind is, for example, a switch disclosed in Japanese Patent Laying-Open (Kokai) No. Heisei 10-200550.
On the other hand, a function provided by VoIP (Voice over IP) and the like enables telephone voice to be accumulated by Internet and telephone service providers have made a move toward realizing a telephone network by Internet. Requirements and conditions for QoS assurance in Internet have accordingly become more stringent in recent years.
FIG. 8 shows a structure of a conventional switch. With reference to FIG. 8, the conventional switch includes an input port unit 810 for receiving data and a switch unit 820 for executing switching processing. Although the input port units 810 exist as many as the number of ports of the switch unit 820, only one port unit is illustrated here for the convenience of explanation. The input port unit 810 includes a buffer 811 for temporarily holding input data. The switch unit 820 includes a switch core 821 for switching and outputting data applied through the input port unit 810 and a scheduler 822 for setting connection of the switch core 821 to control switching.
In thus structured conventional switch, the input port unit 810, upon receiving input data, holds the data in the buffer 811 and for requesting connection of the data to an output destination, sends a request for connection to the output port to the scheduler 822.
The scheduler 822 examines a connection request received from each input port unit 810 to conduct switch scheduling so as to prevent connections from the input ports to the output ports colliding from each other. Then, according to the scheduling results, the scheduler sets a connection of the switch core 821, as well as returning a grant signal indicative of connection allowance to the input port unit 810.
The input port unit 810 having received a grant signal from the scheduler 822 transmits data directed to the output port of the connection destination notified by the grant signal to the switch core 821 of the switch 820. Then, the switch core 821 conducts switching according to the setting by the scheduler 822 and transmits the received data to each output port.
In switch scheduling according to the above-described conventional technique, however, uniform scheduling is conducted taking none of quality and priority of data to be switched into consideration. It is therefore impossible to realize switching according the quality of traffic when such traffic as telephone voices whose delay characteristics are imposed severe requirements is transferred through Internet and when traffic having a plurality of protocols whose quality and characteristics are different is accommodated in one switch.
Under these circumstances, proposed is a switch which, with information indicative of priority applied to data, conducts scheduling in accordance with the priority by a scheduler. Conventional technique of this kind is, for example, disclosed in Japanese Patent Laying-Open (Kokai) No. Heisei 8-56230. The literature discloses a switching system which realizes switch scheduling according to priority. The switching system disclosed in the literature schedules traffic of every priority simultaneously by one scheduler.
As described in the foregoing, since conventional switch scheduling is uniform taking none of quality and priority of data to be switched into consideration, there occurs a case where switching in accordance with quality of traffic can not be realized.
Also with respect to the switching system recited in Japanese Patent Laying-Open No. Heisei 8-56230 which realizes switching scheduling in accordance with priorities, since scheduling is conducted by one scheduler which determines all the priorities, the system structure is complicated. Another shortcoming of the system is that special scheduling algorithms are required for simultaneously conducting scheduling in response to connection requests of all the priorities, which makes flexible change of setting impossible.